Thermionic amplifier



Janfsb, 1945. r R DOME 2,368,454

THERMIIONIC AMPLIFIER Filed Jan. 23, 1943 UTILIZATION M05 DEV/CE Fla-905m) BAA/0 J'OURCE 0F SIGNALS I n e n t 0 1r Robert B. Dome,

His Msowney.

Patented Jan. 30, 1945 Robert B. Dome, Bridgeport, Coma, assignor to General Electric Company; a corporation of New York Application January 23, 1943, Serial N... 173,361

2 claims. 7 (Cl. 1i9 1-r1) My invention relates to thermionic amplifiers and particularly to such amplifiers which include two or more electron discharge devices connected in cascade and provided with grid bias resistors in their cathode circuits which tend to produce degeneration.

The necessary negative grid bias voltage with respect to the voltage of the cathode in electron discharge devices employed in thermionic amplihers is frequently obtained by providing a resistance in the cathode circuit between the cathode and ground. Any alternating current voltages appearing across thecathode resistor are in phase with the signal voltages impressed on the grid or control electrode and result in degeneration of the amplifier with respect to the signal voltage. For this reason, it is common practice to by-pass the cathode resistor with a condenser so that little if any voltage corresponding to the alternating current variations appears across the cathode reslstor. When two or more amplifiers are connected in cascade, it has been found possible to avoid the necessity of providing by-pass condensers for the cathode resistors by utilizing available regenerative voltages in such a manner that the degenerative voltages in the cathode resistors are neutralized.

It is an object of my invention to provide a thermionic amplifier including two electron discharge devices connected in cascade and provided with an improved arrangement for overcoming the degenerative efiects in the cathode resistors and for increasin the frequency range of the amplifier.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further ob- J'ects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing, the single figure of which represents a two-stage thermionic amplifier embodying my invention. I

Briefly, the amplifier shown in the drawing comprises two electron discharge devices, resistance coupled in cascade; both devices are pro vided with resistors in their cathode circuits for obtaining the necessary bias voltage for their control electrodes. Instead of providing condensers by-passing the cathode resistors to prevent the impressing of degenerative voltages between the control electrode and cathode, a voltage which is regenerative with respect to the signal impressed on the first device is fed back by a resistance from the cathode of the second device to the cathode of the first device. The value of the resistance is selected so that the regen- 6 erative voltage fed back to. the first device not only overcomes the degenerative voltage due to the cathode resistor of the first device but also provides sufiicient regenerative voltage to in-v crease the output of the first device to such an extent that the output si al of the second device is not'less than it would he were a condenser provided to'by-pass the cathode resistor of the second device to prevent degeneration. This circuit makes it possible to omit two by-pass condensers and the cost and weight of the circuit is reduced. Better over-all performance is obtainable because the circuit may beadjusted to give the same efiect as would be obtained by complete bya sing of the cathode resistors by condensers having infinite capacity; it follows that the response of the amplifier at low frequency is increased. In or-': der to increase the response of the amplifierat higher frequencies and to reduce the loss of gain in the higher frequency range, the resistance coupling the cathodes of the two electron discharge devices is shunted by a condenser which increases the feed-back of high frequency regenerative voltages.

Referring now to the drawing, the amplifier comprises a first electron discharge device in having a cathpde ii, a grid or control electrode i2, and an anode i3. Signals within the wide frequency range are supplied from a suitable source it and impressed upon the grid it through a coupling including a condenser. l and a resistor 16. Negative bias :ior the control electrode i2 is provided by a cathode resistance ll between the cathode ii and ground. Anode voltage for the device It is obtained from a suitable source such as a battery it connected to the anode through an output resistance it. The output voltage of the device Ml is coupled to a second electron discharge device 20 having a cathode 2i, a rigid or control electrode 22, and an anode 23. The anode E3 of the device ill is coupled to p the control electrode of the device 20 by a condenser 25 and a coupling resistor 26; the devices lil and 2B are thus connected in cascade. The anode voltage for the device 20 is also obtained from the battery 18 which is connected to the anode 23 through a load resistance 21, and the output voltage of the device 20 is coupled to a suitable utilization device 28 by a condenser 29. B8 The device 20 is provided with a resistance 30 in its cathode circuit for obtaining the required cathode 2| is connected to the cathode H by a resistance 3|. The value of this resistance. is selected so that a'portion of the voltage appearing across the resistance 30 isjed back. and impressed across the resistance III,- This voltage is 180" out of phase withnthe voltge generated in the resistance l1 and, therefore,- tends to neutralize; any degeneration due to voltages produced by the cathode current of the device 0. The value of the resistance 3| is selected sqthattheyoltage, impressed uponthe cathode LI from he cathode: 2| is sufiiciently great to provide regeneration in the device l and increase its output by an amount sufiicient to compensate for degeneration produced in the device 20 due to the cathode re-r sistance 30, it being understood that the regenerative feed-back will-be made sufiicient' to provide an output fqrdevice 20- equal= to or even greater thanits output wouldbe were any-pass condenser provided for the resistor 30a I have found that the-range of the high frequency response of the amplifier may be extendedsuhstantially hyproviding a small.con-. denser 32' across the resistance 3h When the. amplifier shown in-thedrawing isprovidedwith. the condenser. 32. itslrange ofirequency response for a predetermined. gain.- is increased beyond. that obtainable. in the same amplifien without the resistance 31. and condenser 32, but; provided with by-passr condensers. for the. resistances; i1. and fl.

The valueoithe resistance 3i m ybe obtained. by, connecting. an alternating. urrent. oltmeter.

2,sce,4o4.

the device no was one-half 0'! a senior double-- triode and the device 20 was the other half across the resistance l 1. and adjusting resistance 3i until minimum voltage appears across the resistance l7. This adjustment: provides, neutralization of the loss due to,deg;eneration in the rresistance H. In order lac-neutralize, the loss 1 due.v to degeneration in the. resistance 30 at ,the second, amplifying device 20, thevalue. of resistancefii. is still further decreasedto .a point such that the. over-all gain of the ampliiien-isthe same as it, was found to be with resistance omitted and; by-pass condensers provided for. the resistances I1 and.30. After the. correct value forthe resistance 3] hasheendetermined,afixed resistor of, this valueis employed.

Obviously further electron discharge, devices may be connected in cascade in the same man ner, the neutralization being efiected in stages,. the values of the resistance (correspondingto resistance 31) of eachfstage beingdetermined in the manner described above. g

For purposes ofiillustration but not by way of.vv limitation, there are tabulated below, thehvalues of the resistances andcapacitors employeduin a circuit as illustratedingthe drawingin which thereof.

Resistor:

I I6 -r ..megohm 1 i1 hms 1,000 l9 do 5,600 26 me8ohm 1 21 v 215-- 5,600 3 o 1,000 3| w do 1,800

Condenser:

l5 r. d 0.06 25 0.06 29 0.06 32 maid-..

While I have shown and described my invention inconnection with a two-stage amplifier .em- Playing, two three-electrode electron discharge devices, other applications-will readily he.apparent to those skilled in the art. I" do hottherefore desire my invention to be limited to the particular circuit connectionsshown and described and I intend in the appended claims to cover all mod fit ations withinthe spirit andscopeotmy invention.

What I claim as new and desiretosecure by, Letters Patent of the United States, is:

1. A thermionic amplifier comprising first and,

second electron discharge deviceseach having a cathode and an anode anda control electrode,

means for impressing a signal on the control electrode of said first device, means for coupling saiddevices in cascade, first and second resiste ances connected respectively in the cathode circuits of said first and seconddevices, athird re,

sistance connecting said cathodes for providing a regenerative, voltage at the cathode of saidfirst.

device to substantially neutralize the degeneras tive voltages produced by said. cathode. resistances, and a condenser connected in shunt with said third resistance for increasing the response or said amplifier athigh frequencies.

2; A thermionic amplifier comprisingfirstand second electron discharge devices each having. a cathode andar'ranode and acontrol electrode,

resistance; means for coupling. said devices in cascade first and secondresistances connected.

respectively in the cathode circuitsoi said first and jseconddevices, a third resistance connecting,- said cathodes, and a condenser, connected in.

. CERTIFICATE 0F CORRECTION. Patent No. 2,368,151 January 50,1915.

' RbBEs'r'B. DOME.

It is herein certified that error appears in the printed-specification of the above numbered patent requiring correction as follows: Page 1, sec ond column, line 14.5, for "rigid". rehd -grid---; and that the saie. Letters .Patent sheuldber d with this; correction therein that the same may conform to the record of the case: in the Patent Office. I

Signed and sealed this 1 th'iaay' ofna A. D. 1915.

Leslie Frazer (Seal) v .Acting' Commissioner of. Pate ts; 

